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01-15-2023, 12:56 AM | #1 |
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Hey all, throwing this out there. M550s and M850s run a tire that is around 26.75" OEM diameter. The M5s and M8s run tires that are about 27.75" in diameter.
I've had the M550, two M5s and now have an M850. I feel the tires are just to small for this car - aside from being smaller by an inch in diameter, they also run 8" fronts and 9" rears - as opposed to the M5 & M8 at 9.5" fronts and 10.5" rears. So, in the spring I am looking at new Vossen wheels and going to 9" fronts and 10.5" rears. I'd like to go up one profile, too, to gain that other inch in height (the wheel wells really need to be filled up a bit more - and it would ride a teensy bit better with more rubber in the side wall). I took my M5 snow set down to the tire shop to have a look with them on the M850. They mostly fit, however the offsets are just a bit off, but the inch larger tire really looks good. They said a different wheel with the taller tire would be no problem. I went to my BMW dealership and talked to the tire guy. He waffled about going up a tire size. He checked with the service techs. They said no, don't mess with the OEM diameter. I went to my performance shop guy where I am getting the new wheels. He said don't mess with the OEM diameter. With all the computers, AWD, DSC and what have you, the car could possibly not perform correctly. If you keep the front and rear wheels within a 1% diameter tolerance between axels and go up a profile size, does the car really care if everything is rolling along, but at a 3% or so, different rate of speed on the axel rpm? I know people have gone wider all the time, but you never really hear about changing diameters that much. I know people do this, just don't know what the consequences are, if any, aside from a speedometer that will be slightly off. (I think it would bring the speedo speed closer to the true speed of the car, thus offsetting the 2-3 mph difference built into BMWs - if I remember which way the math works for this application. I could be wrong - maybe it's the other way around, but I don't feel like checking it now.) Any thoughts appreciated. Thx |
01-15-2023, 02:31 AM | #2 |
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BMW or any other German company will expect you to stick to the wheels and tyre sizes they have in their approved list.
If you keep the front and rear circumference as close as the standard tyres are, the car can’t be any the wiser. Will it give you 100% of the experience BMW designed, who knows? |
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01-15-2023, 04:01 AM | #3 |
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I see where you are coming from here and count me among the few who thinks you could be on to something. When considering stagger, I always like to work with revs per mile for a particular tire rather than diamrter; revs/mile is a bit more precise. (I use mfr specs or Tire Rack to get revs/mi.)
So, for instance, going up one size in front and rear (and comparing revs per mile to make sure you are not going to mess up your electronic nannies) will almost always work, at least in the electronic sense. Clearance in the wheel well is a separate issue but generally one size up won't cause problems; working with a good tire shop helps here for test-fitting or whatever. I'm not conversant with the 8er but offhand I see two OE options: 19s with 245/40R-19 & 275/35R-19 and 20s with 245/35R-20 & 275/30R-20. Oh, and now I see you you're proposing a 1.5" width bump both front and rear and an inch wider tire (?) -- that's 25mm -- now you've lost me; I think that is just too extreme. I would think going to 255 front and 285 rear would not be imprudent, but what you're talking about is pretty radical. My two cents.
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01-15-2023, 04:34 AM | #4 |
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just keep rolling diameter same front and rear close and you be fine. more front tire always helps imo
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01-15-2023, 05:13 AM | #5 | |
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The M8 runs a 275 on a 9.5" wheel in front and a 285 on a 10.5" wheel in back. The width isn't the problem. My question still remains about the new height vs OEM. |
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01-15-2023, 05:19 AM | #6 |
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01-15-2023, 05:20 AM | #7 | |
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I don't see a problem with your intended course of action, if -- and only if -- the wider rims don't rub on suspension components, fenders or wheel well. That's where the part about a cooperative and knowledgeable tire seller/shop comes in.
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01-15-2023, 05:43 AM | #8 | |
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The wheels end up about as if I was running a 10mm spacer on my OEMs. Nothing real radical. I just want more meat at each corner and then a little taller if it's doable. Thx for your comments. |
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01-15-2023, 08:40 AM | #9 |
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Increasing overall tire height (diameter) with the same wheel diameter will only decrease the handling capability of your car with respect to turn-in due to slip-angle. If you're looking for increased comfort, you shouldn't have bought a sport model in the first place! Just get a 530i xDrive and leave those snow tires off your M5!
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01-15-2023, 08:55 AM | #10 | |
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01-15-2023, 08:59 AM | #11 |
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The M2 crowd has changed the wheel and tire size. As an example I went from 19X9 and 19X10 to 19X9.5 and 10X10.5 BBS wheels. I increased the tire size from 245/35/19 and 265/35/19 to 255/35/19 and 275/35/19.
BBS called my wheels “Tuner Fitment”. I am not running any spacers and I have zero rubbing.
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01-15-2023, 12:26 PM | #12 | |
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I've taken many 4,000 mile two week trips in the last few years. We go 300 miles/day and try to stay off the freeways. The car is a blast on the two laners, but obviously not M5 territory. It's most noticeable when I push it, but that's not really all that practical with someone else in the car telling you to slow down. (Sheesh. Women...) The wider wheel I am also going to would help negate any increase in tire height. As far as snow tires, sometimes you just need some effing snow tires By the way, these snow tires were an 8" square set from my M550 - and they sucked for a car this big. But, they got me there and back. I bought the car car 2 days before the trip and it's all I could do. Luckily they were still in my basement. But, they are also the recommended BMW snow set for the M850. Same trip, the next day This winter I am running Michelin Alpin4 tires on the OEM wheels.........much, much, much better. Its a twofer: more sidewall plus less wheel gap. I doubt is there is a single M8 owner that says, "Ya know, Ima gonna go down a profile. I just want more space between my fender and the tire." Last edited by snowbimmer; 01-16-2023 at 07:43 PM.. |
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01-15-2023, 12:28 PM | #13 | |
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Front Dia: 27.58" Rear Dia: 27.86" The BMW M5 & M8 snow set uses a 19" wheel and goes down a width to 265 in front, making the gap wider Front Dia: 27.34" Rear Dia: 27.98" The 19" OEM summer set up (which I also ran) was Front Dia: 27.66" Rear Dia: 27.98" In all cases the rears are between 1% to 2% larger in diameter. So, my question, since you bring up x-drive, does BMW engineer the car for this larger wheel diameter in the rear - OR, do they just find the tires that fit within certain tolerances and call it a day? The M850, on the other hand is just the opposite: The fronts are a larger diameter than the rears Front Dia: 26.76" Rear Dia: 26.50" My new setup with 10mm wider tires, and keeping as close to OEM sizing as possible take me to: Front Dia: 27.03" Rear Dia: 26.73" I could then go up one profile, but then I'm pushing 28" diameters, but I could still keep the fronts slightly taller than the rears. And, again, did BMW engineer the M850 with the expectation that the front tires are to be taller than the rears? The Alpina B8, which is a souped up M850, actually uses the taller tires. like the M5 and M8. I think I'll probably just stay within OEM sizing and call it good. Last edited by snowbimmer; 01-16-2023 at 07:41 PM.. |
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01-15-2023, 12:52 PM | #14 |
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If you have not used the tire calculator before here is a link: https://tiresize.com/comparison/
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01-15-2023, 01:14 PM | #15 | |
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This is also good for quick and dirty https://www.discounttire.com/learn/tire-size-calculator This is good for offsets and poke calcs https://willtheyfit.com/ |
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01-15-2023, 02:44 PM | #16 | |
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Also remember those are nominal sizes, not allowing for manufacturing tolerances, (even within the appropriate standards), can be quite wide. BMW could well be setting tolerances which may make front and rear RC (rolling circumference) for the OE tires different than it appears. |
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01-15-2023, 02:51 PM | #17 |
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We had to learn this the hard way in the GT-R world. Many manufacturers and tire size calculators that were "just right" still blew center differentials over and over.
A guy named Shep from ShepTrans (famous in the EVO/DSM/GT-R world for drivetrain) finally gave us the reality. Only way to know for sure is to install the damn tires, and put them on the car at running pressure, and mark them and do a slow rollout. Unless they were REAL close, you'd eventually blow the center diff. BMW's system is probably a little more tolerant. Who knows? I don't be the one to find out. I install either BMW "listed" tires and setups, or I install "square" (same tire all the way round) setups. OP, reality is you can change the OD, but lots of unpredictables can occur as the result. Just giving you a suggested pathway to ensure safety. Shawn |
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snowbimmer6327.00 Llarry21181.00 |
01-15-2023, 04:02 PM | #18 | ||
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I can only base my most experience off my 2 M5s. The OEM 20" summer wheels have a front to back diameter difference of 0.28", or 1.02%. The OEM 19" summer set has a front to back diameter difference of 0.32", or 1.16%. The BMW approved 19" snow set has a front to back diameter difference of 0.64", or 2.34%. (The above based on nominal sizing, because I have no other data to go on) "They" say to always have your front to back diameters within 1% on an AWD car. The OEM summer 20s and 19s are close to 1% (still over), but the winters are are considerably over a 2% difference in diameter. I saw no ill effects during 3 winter seasons, so I'm thinking we may have a little leeway here. And shawnhayes, what did you mean by "REAL" close when you do the roll out? How close is REAL close in Shep's world to not blow out the center diff? Thanks for the input. This is what I've been looking for. |
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01-15-2023, 04:13 PM | #19 |
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I have been driving on B roads and freeways as well as taking some quick corners for 5 days now and I’ve noticed no detriment to handling and ride is much better and much quieter with 40 front and 35 rear sidewalls. I don’t have xdrive. I love the new Continental ExtremeContact DWS06+. It’s an ultra high performance A/S that Tire Rack rated very high and it has great customer reviews as well. I’m very happy with my choice and filled up the wheel well nicely as well as increasing ride height by 1/2” which in these low slung cars certainly not a bad thing.
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01-15-2023, 04:16 PM | #20 | |
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Damn, that sure looks good. I had a Donington M5 - my favorite color. Skyscraper is close. |
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01-15-2023, 05:06 PM | #21 | |
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If you put them on the car, and mark where the tires are, and do 3-10 revolutions, if they are within 1% of the rotation (3.6 degrees) I feel pretty confident they'd be perfectly safe. You'd be shocked how much different 3.6 degrees x 10 rotations looks like. (Imagine 36 degrees of difference between the marks on the tires). So, 1%, probably okay. Shawn |
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01-15-2023, 05:17 PM | #22 | |
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Transfer cases in the current M models have much more 'RWD only' engagement. The BMW M VTG control only applies torque to the front axle/wheels in limited situations. This means the multidisc clutch is running open much more of the time. This at least partly explains how BMW can be more flexible with M model tire selection. Even in the more regular models, there are technical features to improve heat management and reduce wear. Plus changes to oil levels and flows, which reduce churning losses, aids efficiency. |
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